Which of the following statements about electromagnetic waves is correct?
- AAll electromagnetic waves have speeds in air of approximately $3 \times 10^{8}\,\text{m s}^{-1}$.
- BIn air, some electromagnetic waves travel faster than light.
- CThe electromagnetic waves with the largest wavelength are in the infra-red region.
- DThe electromagnetic waves with the smallest wavelength are in the X-ray region.